For Ummihat-ul-Momineen the directives of Parda/Hijab were different and more strict. Therefore, Hazrat Ayesha (rta) had to take extra measures. Secondly, for some time in Medina, other Muslim women were also directed to take extra measures and put on a veil in order to counter the evil schemes of hypocrites of Medina. They were temporary meausures for other muslim women and the context of Surah Ahzab make it clear.
For common Muslim women of today, the requirements of parda are mentioned in Qurah Surah Nur.
Please see:
Discussion 30301